Analysis systems for the photometric determination of an analyte in a body fluid, which use disposable test elements, test carriers, or test strips, are known. They are used in order to determine the concentration of various analytes, such as glucose or cholesterol in blood. The test carriers typically have the form of test strips, however, other forms of test elements are common, such as flat, approximately square plates.
The test carriers typically contain reagents, whose reaction with the sample results in a detectable change, which is measured by means of a measuring and evaluation device associated with the system. In particular, photometric analysis systems are common, in which the reaction causes a color change in a detection layer of the test element, which is measured photometrically. The intensity of the light reflected from the test carrier is typically determined for this purpose.
Upon proper use, the photometric analysis systems typically operate reliably. However, if the required care is not applied by the user upon use of the device or the test carrier and/or test strips, flawed measurement values may result.
Nonetheless, flawed measurement results may also occur upon proper use, in particular if fabrication errors exist in the analysis instrument or in the test carrier. Although great care is used in the production of such analysis instruments and test strips, the need exists to determine malfunctions of the measuring device, in order to avoid flawed analysis values. Because, for example, when determining the concentration of the glucose content, the measurement result is used for the therapy of a patient, in particular to determine the dosing of the insulin, an error-free analysis value is particularly important. An incorrect administration of insulin (excessively low or high insulin administration) based on a flawed measurement result can result in physically hazardous and life-threatening situations.
Analysis systems for optical blood sugar measurement are known in the prior art and are dealt with, for example, in the following publications: DE 101 56 809 A1; U.S. Pat. No. 5,780,304; EP 0 974 303 A1; and EP 0 387 630 A2.
It is typically monitored in the photometric analysis system whether the measuring unit operates error-free. On the one hand, it is verified on the basis of reference values whether the test carrier used is sufficiently wetted. On the other hand, the time curve of the measurement value is verified. For example, it is verified as to whether two chronologically sequential measurement values are monotonously rising anti/or monotonously falling. Upon the chronological recording of multiple measurement values, verifying whether their change re-mains below a specific threshold value is also known.
Erroneous measurement results may sometimes be related to an error in the microcontroller of the analysis instrument. Therefore, many devices are implemented redundantly and comprise two microcontrollers operating in parallel. The use of a second microcontroller (hardware) not only increases the space required in the analysis instrument, it also makes the instrument more expensive. In addition, procedures must be provided for the parallel processing of the measurement signals.
The problem is known in the prior art that the desired concentration value must be concluded from the optically determined measurement values (reflection values). The plausibility check of the concentration values is only performed on the basis of threshold values previously established therein, however.
If the measuring and evaluation device is designed in the form of software, the redundancy may also be provided by a second software module. However, the processing effort is greater, because two programs running in parallel must be executed. In addition, the programming is complex. Determining the analysis result takes longer due to the parallel processing.
It is thus an object of the invention to provide an analysis system for photometric determination of an analyte in a body fluid, which allows a simple verification of the measuring and evaluation device.